The present invention relates generally to gas turbine engines, and, more specifically, to combustor liners therein.
In a gas turbine engine air is pressurized in a compressor and mixed with fuel and burned in a combustor. The combustion gases are channeled through a high pressure turbine which extracts energy therefrom for powering the compressor. A low pressure turbine follows the high pressure turbine for extracting additional energy from the gases for powering an upstream fan in a typical aircraft turbofan gas turbine engine application. In marine and industrial applications, the low pressure turbine instead powers an output shaft.
A typical combustor includes radially outer and inner liners joined together by an annular dome at upstream ends thereof for defining radially therebetween an annular combustion chamber. The dome includes carburetors having corresponding fuel injectors and air swirlers that introduce corresponding mixtures of fuel and air which are ignited for producing the combustion gases in the combustion chamber.
The efficiency of the engine is directly related to the temperature of the combustion gases which temperature is suitably limited for achieving a suitable life of the combustor and hot components downstream therefrom. State-of-the-art high temperature capability superalloy metals are common for modem combustor liners, and are typically protected from the hot combustion gases by having the inboard surfaces thereof covered by a thermal barrier coating (TBC). Conventional thermal barrier coatings are ceramic materials which provide a thermal insulator for exposed inboard surfaces of the combustor which directly face the hot combustion gases.
The combustor liners are further cooled by pressurized air supplied by the compressor. Various cooling configurations are provided for the combustor liners which typically effect film cooling along the inboard surfaces thereof over the thermal barrier coating.
In one typical combustor design, cooling nuggets or rings join together annular liner panels for the introduction of the film cooling air along the full circumference of the liner. A typical cooling nugget includes a radial bridge which joins the aft end of a forward panel to the forward end of the next, or aft panel. A lip extends axially downstream or aft from the aft end of the forward panel and overhangs the forward or upstream end of the next panel to define a cooling slot that extends circumferentially around the liner.
The cooling nugget includes a row of aperture inlets which receive pressurized air from the compressor. The cooling air is channeled through the nugget slots and out an annular outlet at the aft end thereof.
The thermal barrier coating is applied to the liner after fabrication thereof. The multiple panels are firstly joined axially end to end with corresponding cooling nuggets therebetween. The thermal barrier coating is conventionally sprayed over the inboard surface of the combustor liner in a relatively thin and uniform thickness of about 0.4 mm for example. Since the nugget lip overhangs the next adjacent or aft panel, the inboard surface of the lip itself is covered with the thermal barrier coating, but the inside of the slot itself is protected by the lip and is not covered by the thermal barrier coating.
However, the thermal barrier coating is substantially continuous from panel to panel along the inboard surface thereof facing the combustion gases, and the cooling air is introduced through the cooling nuggets themselves which further protects the cooling nuggets from the hot combustion gases. The cooling air discharged from the nuggets flows downstream along the thermal barrier coating on the inboard surfaces of the panels for providing a continuous cooling air film which thermally insulates the combustor liner from the hot combustion gases, and cooperates with the thermal barrier coating for providing enhanced protection of the superalloy substrate metal of the liners.
Although engine efficiency may be increased by increasing the temperature of the combustion gases, the ability to cool the combustor liners with a fixed flowrate of air is limited. Furthermore, it desired to decrease the available cooling air provided to the combustor liners for lowering NOx exhaust emissions.
Although it is possible to increase the thickness of conventional thermal barrier coatings, such thicker coatings can obstruct the proper performance of the cooling nuggets and reduce their cooling effectiveness. For example, the inlet apertures of the cooling nuggets are typically sized to meter or control the flowrate of cooling air channeled through the cooling nuggets. The slot outlet is suitably larger in flow area to ensure unobstructed discharge of the cooling air from the nuggets.
Since the size of the cooling nuggets is preferably limited for limiting size and weight of the combustor, the introduction of thicker thermal barrier coating on the liner necessarily obstructs flow discharge from the nuggets. Without the introduction of such a uniformly thick thermal barrier coating on a combustor liner, the combustor liner will not be uniformly protected from the hot combustion gases.
Accordingly, it is desired to provide an improved combustor liner having thicker thermal barrier coating thereon for enjoying the enhanced thermal protection thereof without obstructing performance of the cooling nuggets.